Models for morality: Temporal semantics for deontic logic
Hess, Stephen Andrew
Grandy, Richard E.
Master of Arts
This work addresses several topics in the semantics of deontic logic. In Chapter One I introduce a standard branching temporal model to serve as the basis for deontic logics and I define three tense operators. I argue that none of the three corresponds to a popular view of the 'will* operator, that the 'will' operator cannot be defined on the model provided, and finally, that the truth conditions for will are exactly those of must.1 In Chapter Two I introduce the monadic and dyadic operators ’O' and ’(-/-)' and review arguments for taking the dyadic as primitive. I show that those arguments do not prove that a dyadic operator is necessary, and that the considerations which led to its introduction are better served by defining conditional obligations with a tense operator 'will always' and the standard truth-functional connectives. I also argue that the 'set of morally acceptable worlds' which deontic semantics use should be construed as a set in which some particular agent fulfills all her obligations. In the third chapter I demonstrate how temporal semantics enable deontic logicians to choose among several formulations of the principles that what is necessary is obligatory and that what is obligatory is possible. I review arguments for rejecting the former as a principle of logic and note a problem which arises when it is rejected. In Chapter Four I demonstrate that an attempt by Richmond Thomason to relate 'dutiful' choices to morally perfect worlds on the temporal model cannot succeed. Finally, I conclude the thesis by investigating the broader implications of the results from the first four chapters.